According to Eskom’s schedule interpretation website, stage 3 increases the frequency of stage 2 by 50%. This means affected areas will be scheduled for load-shedding nine times over four days for two hours at a time, or nine times over an eight-day period for four hours at a time.

Eskom also said it had held an “urgent” six-hour meeting with public enterprises minister Pravin Gordhan after raising load-shedding from stage two to stage four on Monday.

The stage 2 power cuts were caused initially by “generation shortages” and “constraints in diesel supply”, but the need for stage 4 came due to “a further seven generating units that tripped within a period of five hours”.

Eskom said late on Monday night its new Medupi and Kusile power plants – described as the “core of the new build programme” – were showing “a lack of reliability to contribute meaningfully to Eskom’s generating capacity, which is a serious concern”.

At its meeting with Gordhan, Eskom said, a report on the causes of the power shortages, including all the challenges of its new and old power stations, made up the bulk of the discussions between the board, management and the department of public enterprises.

Board chairman Jabu Mabuza said: “We remain uncomfortable about the stability of the generating system but will keep the country informed of our progress over the next few days in providing better assurance about electricity supply.

The power utility started with stage 2 cuts on Sunday, two months after the last round of power cuts hit the country. The blackouts may continue during the week.

President Cyril Ramaphosa said on Monday in an interview with SABC that he was “shocked” by the load-shedding and it had made him "quite angry that we have reached this stage of dysfunctionality”.

“Eskom is a risk. We’ve got all our energy eggs in one basket,” he said.

Ramaphosa announced during the state of the nation address on Thursday that Eskom will be remodelled and split into three state-owned entities dealing with generation, transmission and distribution.

“That is why we are saying, we now need to have a new business model for Eskom where we’re able to minimise the risk, minimise our risk as a nation like other countries have done and unless we do so, we are continuously going to be facing this type of risk,” Ramaphosa said.